Police use force against mostly Syrians on their way to northern Europe

IDOMENI, Greece—After using force against migrants earlier Saturday, Macedonian authorities allowed thousands of migrants to cross the border from Greece, ceding to pressure that has built up in the country in recent weeks amid a huge wave of migrant arrivals on the Greek islands.

On Saturday, efforts by Macedonian officials to let only about 700 migrants a day to cross over from Greece—one-fourth the number of daily crossings seen in recent weeks—were thrown into disarray when a large number crossed an unguarded stretch to...